Solid-state power-conversion system

ABSTRACT

Aspects of the invention overcome a monolithic approach to conventional low-frequency LPTs by using a high-frequency solid-state alternating current ac/ac modular powerconversion approach. Embodiments of the invention enable the ability to incorporate new technologies without in all cases redoing a LPT design from scratch. Furthermore, given that LPTs are for the long term, aspects of the invention ensure that they are durable, efficient, and fault tolerant with overloading capability.

CROSS REFERENCE TO RELATED APPLICATION

This is a nonprovisional application that claims priority to U.S.Nonprivisional Application Serial No. 17/134,178, filed on Dec. 25,2020, now U.S. Pat. No. 11,594,978, as well as provisional patentapplication serial number 62/953,465, filed on Dec. 24, 2019, whosedisclosure is incorporated by reference it its entirety herein.

BACKGROUND

In general, a large-power-transformer (LPT) system is a conventionalapproach and is illustrated in FIG. 1 as a prior art, such as evidencedby a June 2020 publication of “Large power transformers and the U.S.Electric Grid” by the Office of Electricity Delivery and EnergyReliability of U.S. Department of Energy (“June 2012 Publication”). Asillustrated in FIG. 1 , individual parts are not interchangeable witheach other and their high costs (at reduced unit volume) prohibitextensive spare inventories of parts. For example, bushings, oilconservators, radiators and fans, windings and cores and tanks arediscrete parts. As such, on average, only a limited amount of PTs aremanufactured for individual designs. This is because if a change ormodification is needed, the conventional LPT could not be modifiedeasily and modification may need to wait for a while before the update,modification or replacement is installed. This prior approach poses afurther challenge since given that the several existing LPTs arereaching their end of service lives. For example, the average age ofinstalled LPTs in the United States is well over few decades, withmultiple LPTs estimated to be 25 years or older. In addition, the lossof plurality of such LPTs, that form the backbone of U.S. power grid,will clearly run into the problem of energy security related to thenon-availability of sufficient spares exacerbated further by the factthat these spares are not interchangeable for installations at differentlocations. Also, typical voltage ratings of conventional LPT may beillustrated in the following table:

TABLE 1 Typical voltage ratings of conventional LPT. High Side Low Side34 kV 230 kV 161 kV 138 kV 115 kV 69 kV 35 kV 4 kV 765 kV 9 1 1 14 3 7 115 500 kV 3 107 16 43 69 43 3 153 345 kV - 18 27 269 185 136 10 336 230kV - - 87 226 628 422 56 528 161 kV - - - 44 162 336 14 158 138kV - - - - 365 1129 35 476 115 kV - - - - - 390 213 337

Furthermore, procurement and manufacturing of LPTs is a complex processthat requires prequalification of manufacturers, a competitive biddingprocess, the purchase of raw materials, and special modes oftransportation due to its size and weight. The result is the possibilityof extended lead times that may stretch beyond 20 months if themanufacturer has difficulty obtaining certain key parts or materials.Key industry sources—including the Energy Sector Specific Plan, theNational Infrastructure Advisory Council’s “Framework for EstablishingCritical Infrastructure Resilience Goals and the North American ElectricReliability Corporation’s Critical Infrastructure Strategic Roadmap haveidentified the limited availability of spare LPTs as a potential issuefor critical infrastructure resilience in the United States, and boththe public and private sectors have been undertaking a variety ofefforts to address this concern. See also June 2012 Publication.

Due to the significant capital expenditure, long lead time, and uniquespecifications associated with the procurement and manufacturing of areplacement LPT, there is an opportunity to research more flexible andadaptable LPT designs. Although the costs and pricing vary bymanufacturer and by size, a LPT may cost millions of dollars and weigharound hundreds of tons. FIG. 2 illustrates a table showing a typicaloverview of the cost and weights of major parts of the LPT, which issupported by the June 2012 Publication.

Two raw materials-copper and electrical steel-often account for overhalf the total cost of an LPT, see also June 2012 Publication. Forexample, manufacturers have estimated that the cost of raw materialsaccounted for 57 to 67 percent of the total cost of LPTs sold in theUnited States between 2008 and 2010. Of the total material cost, about18 to 27 percent was for copper and 22 to 24 percent was for electricalsteel. The average prices of both copper and steel have increasedsignificantly over the years, as shown in FIG. 3 , which have clearimplications for conventional LPTs and supported by the June 2012Publication. Electrical steel is used for the core of a powertransformer and is critical to the efficiency and performance of theequipment. In addition, copper is used for the windings. In recentyears, the price volatility of these two commodities in the globalmarket has affected the manufacturing conditions and procurementstrategy for LPTs.

Transportation is also an important element of the total LPT cost,because an LPT may weigh hundreds of tons and often requireslong-distance transport. Transporting an LPT is a massive challenge withtransporting conventional bulky and heavy low frequency (LF) (60-Hz aswell as 50 Hz) LPTs. These items have large dimensions and heavy weightpose unique requirements to ensure safe and efficient transportation.Current road, rail, and port conditions are such that transportation istaking more time and becoming more expensive.

Therefore, an improved approach is required as conventionallow-frequency LPTs typically follow a monolithic approach to design dueto historical reasons that need to transition to more modular andflexible (e.g., in voltage, current, power flow) designs with ability toseamlessly/near-seamlessly scale. Given that the cost of raw materialshas continued to increase, existing LPTs are high in transportabilityand transportation cost.

SUMMARY

Aspects of the invention overcome a monolithic approach to conventionallow-frequency LPTs by using a high-frequency solid-state alternatingcurrent ac/ac modular power-conversion approach. Embodiments of theinvention enable the ability to incorporate new technologies without inall cases redoing a LPT design from scratch. Furthermore, given thatLPTs are for the long term, aspects of the invention ensure that theyare durable, efficient, and fault tolerant with overloading capability.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Persons of ordinary skill in the art may appreciate that elements in thefigures are illustrated for simplicity and clarity so not allconnections and options have been shown. For example, common butwell-understood elements that are useful or necessary in a commerciallyfeasible embodiment may often not be depicted to facilitate a lessobstructed view of these various embodiments of the present disclosure.It may be further appreciated that certain actions and/or steps may bedescribed or depicted in a particular order of occurrence while thoseskilled in the art may understand that such specificity with respect tosequence is not actually required. It may also be understood that theterms and expressions used herein may be defined with respect to theircorresponding respective areas of inquiry and study except wherespecific meanings have otherwise been set forth herein.

FIG. 1 is an illustration of a large-power-transformer (LPT) system ofthe prior art.

FIG. 2 illustrates a table showing a typical overview of the cost andweights of major parts of the LPT.

FIG. 3 illustrates a chart showing average prices of both copper andsteel have increased significantly over the years.

FIG. 4 a illustrates a schematic of a single-phase system according tosome embodiments.

FIG. 4 b illustrates a schematic of a single-phase system havinginductors and transformer aspects of the invention.

FIG. 4 c illustrates a schematic of a two-level system aspects of theinvention.

FIG. 4 d illustrates a schematic of a switched-capacitor system aspectsof the invention.

FIG. 4 e illustrates a schematic of a soft-switching topology systemaspects of the invention.

FIG. 5 illustrates a N-time replicated single-phase system for N-phaseoperation aspects of the invention, where N=3.

FIG. 6 illustrates a schematic for a single-phase voltage scalingpathway aspects of the invention.

FIG. 7 a illustrates a schematic for a voltage scaling system having acascaded N-phase system according to some embodiments.

FIG. 7 b illustrates a schematic for a voltage scaling system with Nthree-phase ac/ac modules according to some embodiments where N = 3.

FIG. 8 a illustrates a diagram for controlling a single-phase system inresponse to a N-phase system according to some embodiments.

FIG. 8 b illustrates a diagram for controlling a single-phase systembased on an optimal control of switching states according to someembodiments.

FIG. 9 a illustrates a diagram for a ring architecture of control of aphase-based ac/ac according to some embodiments.

FIG. 9 b illustrates a diagram for a mesh architecture of control of aphase-based ac/ac according to some embodiments.

FIG. 10 illustrates a schematic of a conventional LPT according to priorart.

FIG. 11 a illustrates a diagram for a high-frequency-based solid-statetransformer (SST) system having a set of power-electronic converteraccording to some embodiments.

FIG. 11 b illustrates a diagram for a high-frequency-based solid-statetransformer (SST) system having a set of power-electronic converteraccording to some embodiments.

DETAILED DESCRIPTION

Embodiments may now be described more fully with reference to theaccompanying drawings, which form a part hereof, and which show, by wayof illustration, specific exemplary embodiments which may be practiced.These illustrations and exemplary embodiments may be presented with theunderstanding that the present disclosure is an exemplification of theprinciples of one or more embodiments and may not be intended to limitany one of the embodiments illustrated. Embodiments may be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure may be thorough and complete, and may fully conveythe scope of embodiments to those skilled in the art. Among otherthings, the present invention may be embodied as methods, systems,computer readable media, apparatuses, or devices. Accordingly, thepresent invention may take the form of an entirely hardware embodiment,an entirely software embodiment, or an embodiment combining software andhardware aspects. The following detailed description may, therefore, notto be taken in a limiting sense.

High-frequency solid-state power-conversion system

Referring now to FIG. 4 a , a single-phase module of the aspects of theinvention is shown. In one embodiment, the single-phase module mayprovide a basic building-block to work with or without an isolatedtransformer. For example, magnets or magnetic force sources (e.g.,electromagnets) may be provided as an external, separate or a discreteelement. In another embodiment, the magnetic source illustration in FIG.4 b may be a magnetic core that includes the high frequency transformer,the capacitor, and the inductor as a single core. In some embodiments,they may be integrated as illustrated in FIG. 4 b .

Still referring to FIG. 4 a , the single-phase system 400 comprises twosets of blocks 402 and 404 for the single-phase realization that areconnected in series at the input as well as at the output sides. In oneembodiment, the input and the output may be both alternating current(ac) power signals that may have different magnitudes.

In one embodiment, in each block 402 or 404, when an input side switch(e.g., Q_(a1)) turns on, the fluxes of the input and output inductors(e.g., L_(a1) or L_(a2)) are built up. On the other hand, if an outputside switch (e.g., Q_(a2)) turns on, then, the energies of the inductorsmay be transferred to an ac-link capacitor (e.g., C_(a2)) and an outputcapacitor (e.g., C_(a4)). The frequency of the ac may also havedifferent values for different needs.

For example, the American grid frequency is 60 Hz nominally, but it mayvary a bit around that nominal frequency. Further, in anotherembodiment, Asian countries may be 50 Hz in places. However, in otherapplications, such as aerospace applications, the frequency may be 400Hz.

The switching schemes of two devices, such as majority-carrier deviceslike field effect transistors and/or minority carrier devices. In thisexample, the switching in each block of the single-phase module 400 maybe different. For instance, in one scheme, all of the four switches inthe two blocks may be switching under high frequency. In another scheme,while the two switches of one block may be operating under highfrequency, the two switches of the other block may be static inswitching state. In yet another scheme, one may achieve a mixedcombination of these two switching schemes. It is also noted that, whilethe ac/ac single-phase topology in FIG. 4 a may be hard-switched forsome switching states, soft-switching for additional loss mitigation ispossible by using a combination of possibilities.

In one aspect, the magnetics may be magnetic-core based and/or may beair-core based. In another embodiment, even though the basic buildingblocks shown in FIG. 4 a is a two-level embodiment, three orhigher-level variants may also be included, as illustrated in oneembodiment in FIG. 4 c . Additionally, even though FIG. 4 a mayillustrate one embodiment that is based on an inductor and capacitorpassive-based approach, a switched-capacitor approach solely relying oncapacitors may also be a variant of the same architectural approachshown in FIG. 4 a . This approach is shown in FIG. 4 d . In thisembodiment, aspects of the invention may be shown with a phasestaggering. For example, in an isolated switched-capacitor approach, aswitch may be used to switch to each ac/ac module in response to anappropriately time phase shifted to reduce the ripple and reducingmagnetic passive size.

For the embodiment using the isolated transformer, the size of thehigh-frequency based transformer solution significantly reduces the sizeof the transformer obtained using a conventionallow-frequency-transformer approach as used in conventional LPTs due tothe rise in frequency may reduce flux cycle, which in turn reduces thecore size. Switches Q_(a1)-Q_(a4) are not limited to field-effecttransistor (FETs), as illustrated. In one embodiment, the switchesQ_(a1)-Q_(a4) may be of different structures (e.g., insulated-gatebipolar transistor (IGBT), junction gate field-effect transistor (JFET),metal oxide silicon field-effect transistor (MOSFET), or bipolarjunction transistor (BJT)) and may be of different material base (e.g.,GaN, SiC, Si, GO_(x)). In one aspect, the basic topology of a block inFIG. 4 a may have variance, and the architecturalinput-series-output-series system is realizable using other lower- andhigher-order power-converter topologies as well. For example, buck orboost basic or derived topologies such as Zeta or Sepic topology.

For instance, one embodiment of soft-switching topology is captured inFIG. 4 e . In one embodiment, the soft-switching circuit may be used asa loss-mitigating soft switching circuit. In another scheme, instead ofusing an ac-link as a capacitor only, one may use aninductive-capacitive link instead of the capacitor. In one example, theinductive part of the link may be an external inductor and/or theparasitic inductance of the isolating transformer itself. The inductivelink in another embodiment may be in series with a switch as well. Inanother embodiment, it may be also use resonant, quasi-resonantzero-voltage-switching, zero-current-switching, evenzero-voltage-zero-current-switching auxiliary circuits that suitablyembedded in the core topology shown in FIG. 4 a .

Still referring to FIG. 4 a , in one embodiment, a single-phase systemmay include a single-stage topological ac/ac illustration withbidirectional power-flow capability. In this aspect, ac input is fedbetween A_(in) and A′_(in) while ac output is sourced between A_(out)and A′_(out). In FIG. 4 b , a variation system 410 of FIG. 4 a mayinclude inductors and transformer in each block monolithicallyintegrated to reduce size and ripple.

Referring to FIG. 4 c , another multilevel variant illustration 420 ofthe two-level block shown in FIGS. 4 a and 4 b . Referring to FIG. 4 d ,another Illustrative embodiment 430 of two ac/ac modules connected in acascaded configuration. Unlike FIG. 4 a , each ac/ac module may notcomprise the inductors. Instead, the modules may be operated usinginterleaving (or phase staggered). For example, interleaving or phasestaggering may include the switching of each ac/ac module is shiftedTs/N where Ts is the switching period and N is the number of ac/acmodules. With this approach, ripple may be reduced and that magneticssize may be reduced.

In one embodiment, the FIG. 4 d may identify 2 modules, modules 432 and434. the aspects of the invention may be extendable to multiple modules.The input and output inductors (e.g., L_(a11) and L_(a12) and L_(a21)and L_(a22), respectively) may be realized in plurality ofconfigurations. For instance, they may be discrete or they may becoupled on the input and output sides or they may all be coupled.Depending on the application, only one inductor on the input and outputside may suffice as well.

Referring now to FIG. 4 e , another embodiment illustrates anotherconfiguration 440 for reducing semiconductor loss of the basicrealization shown for instance in FIGS. 4 a and 4 b . The add-onsoft-switching (SS) circuit 446 for each block (e.g., 442 and 444) ofthe overall ac/ac module 440 is illustrated. It is noted that, dependingon the application, added capacitance may be needed across each of thetwo main devices (e.g., for O_(a11) and Q_(a21)) in each block 442 or444 to enable SS. Also, the SS devices 446 in each block 442 or 444(e.g., Q_(ass12) and O_(ass21)) may be other type of appropriatereplacement, which may include bipolar and/or narrow-/wide-bandgapdevice (e.g., Si IGBT with antiparallel diode). Also, the SS circuit 446may include inductors (e.g., L_(ass11) and L_(ass21)) in each block 442or 444 may be discrete or coupled or coupled to the transformer. In oneembodiment, an auxiliary inductor for soft switching may be discrete(i.e., one on each core) or may be combined (coupled) onto a single coreor 2 inductors may be coupled to the same core that also hosts thetransformer. In a variant of FIG. 4 e , these solid-state (SS) circuits446 may be SS inductors and these may fully or partially absorbed (e.g.,as a leakage inductance) in the transformer of the same block.

In one aspect of the invention, modular scalability of the basic ac/acinnovations is multifold. For example, modular scalability may apply tonumber of phases, voltage levels, and current levels. Regarding amulti-phase operation, the modular scalability may have differentpathways, which are discussed below. One such example may include anexample of the single-phase building system shown in FIG. 4 a for Ntimes for N-phase operation. In such an example, thus, for a three-phaseoperation (i.e., with N = 3), a system 500 may include three of thesingle-phase modules (shown in FIGS. 4 a through 4 e ) are needed.Alternately, N-phase system may also be realized using N blocks asillustrated in FIG. 5 for a three-phase system (i.e., with N = 3),having blocks 502, 504, and 506.

In one example, the three-phase design system shown in FIG. 5 mayinclude 3 blocks with 2 switches per block. In this embodiment, theswitches in each of the clocks may be switching under high frequencycontinuously OR they may be sometimes switching under high frequencyfollowed by a time duration when they are not operating under highfrequency and may not change switching state.

In another embodiment, the multi-phase scheme may build upon theswitching scheme outlined for the single-phase system shown in FIG. 4 a. For example, the multi-phase approach may be extended the same waywith regard to all switches of the N blocks, thereby including thepossibilities that for the N-phase system operation may be enabling allof the switches switching under high-frequency condition all the time.In another embodiment, some of the switches operating under highfrequency while some of the switches not changing switching state, or anarbitrary combination of these two switching possibilities.

In one aspect of the invention, the single-phase system in FIG. 4 a mayalso be able to handle loss mitigation. For example, mechanisms of lossmitigation using soft-switching for single-phase system variant shown inFIG. 4 a may also be extendable to the N-phase scalable version as well.In another embodiment, even though the reference for multi-phaseextension is so far referred to the topological variant in FIG. 4 a ,aspects of the invention may extend for topological extensions and/orvariations of the basic ac/ac module, as detailed earlier with someillustrative embodiments provided in FIG. 4 a .

In another embodiment, the system in FIG. 5 may also include aspects ofthe invention shown in FIGS. 4 b, 4 c, 4 d, and 4 e . In other words,the blocks in the system in FIG. 5 may incorporate the various featuresof FIGS. 4 b, 4 c, 4 d, and 4 e . In another embodiment, theincorporation may be selective; for example, the incorporation of thevarious embodiments may be individually or discretely incorporated.

With regard to voltage scalability, there are several pathways. One ofthe pathways may need to cascade the single-phase system shown in FIG. 4a as illustrated in FIG. 6 . FIG. 6 may be a voltage scaling approachhaving a single-phase ac/ac system as the building block according tosome embodiments.

In FIG. 6 , a schematic illustrates a single-phase system 600 havingac/ac modules 602, 064, and 606 for the single-phase voltage scalingpathway. For example, each “ac/ac” block, such as 602, may be asingle-phase system as illustrated for one embodiment in FIG. 4 a . Forexample, the output of each ac/ac voltage may be added up for voltagescaling. In another embodiment, variant may be a single-phase ac/acscaling is to follow a similar approach as the previous scheme with anexception that the inductors and capacitors (LC) filters at the inputand output of each block may not be repeated for each ac/ac block inFIG. 6 .

In another embodiment, the system in FIG. 6 may also include aspects ofthe invention shown in FIGS. 4 b, 4 c, 4 d, and 4 e . In other words,the blocks in the system in FIG. 6 may incorporate the various featuresof FIGS. 4 b, 4 c, 4 d, and 4 e . In another embodiment, theincorporation may be selective; for example, the incorporation of thevarious embodiments may be individually or discretely incorporated.

Instead, FIG. 7 a illustrates a schematic showing a system 700 thatbuilds on the system shown in FIG. 4 a . In one example, the system 700may include the LC filters at the input and output of the block and theinput and output voltage of the reduced-order block is added in cascadedconfiguration and finally the LC filters are placed for the overallmultilevel unit at the overall (or even intermediate) input and theoverall output ports. Also, the cascaded single-phase ac/ac system maybe replicated for N sets to realize an overall N-phase system. Inanother embodiment, the reference for multi-phase extension is so farreferred to the topological variant in FIG. 4 a . In one aspect, oneembodiment may include topological extensions and/or variations of thebasic ac/ac module, as detailed earlier with some illustrativeembodiments provided in FIG. 6 .

Other aspects of the invention may include a variation of voltagescaling. Referring now to FIG. 7 a may include a system 700 having ageneralized approach where an entire N-phase system is cascadedaccording to some embodiments. In one embodiment of such an approach forN = 3 (i.e., a three-phase system) is illustrated in FIG. 7 a for nthree-phase ac/ac modules, such as 702, 704 and 706. FIG. 7 billustrates a schematic of a system 710 that builds on the system 700 ofFIG. 7 a with a more detailed illustration for n = 3 shown in FIG. 7 b ,such as 712, 714, and 716. In one embodiment, the system 710 maydemonstrate the ability for scaling for additional N-phase systems aswell.

In another embodiment, the current scaling approach may be done by aplurality of options including paralleling multiple switches in a blockand/or paralleling multiple blocks and/or multiple ac/ac modules inparallel and/or paralleling the entire ac/ac system. Additionalvariations on these approaches following some of the FIG. 4 approachesare also feasible.

In some aspects of the invention, controls and protections aspect of thepower-electronic system may be further described below. For example,while the switching (or modulation scheme is discussed earlier), theseswitching may enable different output in response to controls andperformance objectives desired out of the power system. In oneembodiment, the mechanism for control may be based on proportionalresonant and/or harmonic compensators (PRCs) with transformation toalleviate the impact of nonlinear gain.

One such embodiment is a diagram shown in FIG. 8 a for a N-phase systemwith N = 3, where the three-phase load may be a load or the output ofthe ac/ac converter system. The modulation scheme may be linear,nonlinear, or hybrid. For example, at 802, 3-phase output-voltagereference(s) and at 804, 3-phase output-voltage feedback(s) are providedas a load at 806.

In accordance with other embodiments, yet another approach may be basedon an optimal control of the system switching states. FIG. 8 b mayinclude a flow chart for controlling a single-phase system in responseto a N-phase system according to some embodiments. In one embodiment, at820, it is determined whether feasible switching sequences of the ac/acblock or system. Switching sequence is time evolution of switchingstates. Essentially, each switch turns on (say a binary state of 1) oroff (say a binary state of 0) (so there are typically binary states ifone ignores the transition time which is quite small). A switchingsequence could be 0 followed by 1 or 1 followed by 0 or 0 followed by 1followed 0 etc. A feasible switching sequence is a subset of allpossible switching sequences for a power converter.

At 824, it is further determined whether reachable switching sequencesusing stability criterion. At 826, embodiments of the invention solve acost optimization problem that under stability bound may lead to singleor a union of optimal reachable switching sequences. In one embodiment,the switching sequence control may have 3 main elements: a predictivemodel, system constraints, and an optimization problem that translate tominimizing/maximizing a single or multi-objective cost function. In eachtime horizon, a switching sequence is chosen and the chosen sequence mayminimize the cost function using the prediction of the model and withinthe allowable constraints. In another embodiment, a cost function may beto differentiate between desired voltage and actual voltage and/or powerconverter loss (that needs to be minimized).

Once it is solved, an optimal function may be switched to an ac/acsystem or a block of system in accordance with the solved solution at826. In another embodiment, the output may also provide to a sensor or afeedback loop or an estimation back to further fine-tune the costoptimization at 828. In a further embodiment, a hybrid model of theac/ac system or block of the system may be switched at 830 beforetriggering the solution.

In one embodiment, aspects of the invention provide an optimal costfunction that addresses the performance metrics (e.g., efficiency, totalharmonic distortion, regulation, power control, electromagneticinterference noise) that need to be realized and then may minimize ormaximize this cost function using a predictive model and under systemconstraints to generate the switching states and hence switchingsequences. To reduce the computational overhead in real time, theswitching sequences may also be synthesized offline under stability(and/or reachability constraints).

In yet another embodiment, an extension of the control from an ac/acmodule level to plurality of ac/ac modules of a multi-phase system mayinclude multiple pathways of realization ranging from hierarchical todistributed to pseudo-decentralized control with limited communicationto realize local (ac/ac module) and global (overall multi-ac/ac-modulesystem) control objectives. In one example, to differentiate local andglobal control objectives, one may implement an actual global controllerwhich may coordinate with multiples local controllers that command thepower converters. Alternately, each controller may have a localcontroller while the global controller may be distributed among thelocal controllers and coordinated on a cyber layer thereby needing adedicated global controller. Local control objectives has been alludedto above. In another embodiment, the local or global controller may bein the form of a physical hardware device dedicated for the controlparameters. In another embodiment, the functions of the local or globalcontroller may be implemented by software or programs.

In another embodiment, global control objectives may have plurality ofobjectives including but not limited to load sharing, voltage sharing,interleaving etc., to name a few. For communication-based coordination,aside from protocol-based communication, and communication mechanism mayalso be based on information compression, coding,event-/self-triggering, etc., to reduce the rate of data and informationexchange among the ac/ac modules.

In one embodiment, FIG. 8 a may illustrate a linear control scheme for aN-phase system with N = 3. In another embodiment, the FIG. 8 b may be anoptimal and/or nonlinear control scheme for the ac/ac system or itsblock. In another embodiment, the control scheme is configured toreceive input or instructions from a user. For example, the user mayprovide the instructions as programming codes. As such, switch controlsfor the control scheme may receive these codes or instructions from theusers and the switch controls may process these instructionsaccordingly. In one embodiment, the switch controls may include agraphical user interface (GUI) that may be designed to receiveparameters or data from the control schemes shown in FIGS. 8 a and 8 bso that a user may control or select effectuate the control schemes. Inanother embodiment, the parameters from the control schemes in FIGS. 8 aand 8 b may further be configured as inputs to application programminginterface (API) so that other programs or software may interface thecontrol schemes to enable easy manipulations of the controls. In afurther aspect, the parameters or controls may be in the form of digitalcontrol modules, units, or devices. In another embodiment, the controlsmay be analog devices. In another embodiment, the controls may be acombination of digital and analog devices. In yet another embodiment,the control devices may further include wireless capabilities totransmit or receive the parameters or data thereof via wireless signals.

Referring now to FIGS. 9 a and 9 b , a ring architecture 900 and a mesharchitecture 920 are illustrated as two of such embodiments. Modularextension of the control approach from a single ac/ac N-phase system tom-module N-phase ac/ac system is achieved using networking where thenetwork architecture and (wired/wireless) communication protocol may beone arbitrary type. For instance, and as illustrated in FIGS. 9 a and 9b , the mesh 920 and ring 900 architectures are illustrated as two ofsuch embodiments. The modular system may have the ability to achievefault tolerance and/or self-healing for scenario when communicationbreakdown occurs or even ability to operate without communication orusing event-triggered communication. Another control aspect of theinvention may relate to the protection of the ac/ac standalone andmulti-module system for plurality of phases and modules. In anotherembodiment, the protection may include three separate elements:protection against faults on the input and output ac sides, protectionof the ac/ac converter system, and a coordination among these two setsof protections. Aspects of the invention improve over the coordinationpart by leveraging the high-speed protection capability of the ac/acpower-electronic system to reduce stress, cost, and enhanced reliabilityof the input and output ac side protections. In one embodiment, theprotection may be configured where the solid state ac/ac powerconversion system may be fed by an ac input and output an ac output witha power converter right in the middle to enable this. A fault may occuron the input and/or the output ac side(s). For example, line to groundfault or line to line fault, etc. A fault may also happen in the ac/acconverter itself. In either case, rapid action including fastcoordination may be considered so that the impact of the fault isquickly mitigated.

Comparison of the Proposed Innovation With Other Solid-State-Transformer(SST) Technologies

FIG. 10 may include an illustration of a conventional LPT. In thisexample, the LPT includes a 60-Hz flux cycle. In one aspect, theillustration of flux cycle may be a 50 Hz in conventional LPTs. Aconventional 60/50 Hz cycle-based LPT has no active semiconductordevices. Because flux cycle 1002 of the transformer is real low (e.g., atypical low frequency 60/50 Hz LPT has a low flux cycle compared to thesolid state transformer which switches on the order of 20,000 if nothigher), the size and weight of the LPT is significantly high.Conventional low-frequency LPTs have limited flexibility, modularity,and scalability. It is noted that, in some cases, a secondary side 1004of a conventional 60/50-Hz cycle LPT may be modified with secondary-sidepower-electronic tap changing regulators. However, even such a LPT haslarge size and heavy weight since the flux cycle is still low.

The weight and size reduction of a 50/60 Hz cycle LPT is reduced byincreasing the frequency of the LPT flux cycle to yield ahigh-frequency-based solid-state transformer (SST). However, to obtainsuch high frequency in a SST, a set of power-electronic converter, asillustrated in FIGS. 11 a and 11 b , may be needed at the input side andat the output side of a high-frequency (HF) transformer. There aredifferent ways to achieve this.

According to aspects of the invention, according to FIG. 13 a , afront-end power-electronic converter 1100 may be alow-frequency-ac-to-high-frequency-ac single-stage (LFAC/HFAC) converter1102, which may also be referred to as a cycloconverter. Similarly, atthe output, one may use a high-frequency-ac-to-low-frequency-acsingle-stage (HFAC/LFAC) converter 1104, which may also be asingle-stage cycloconverter.

In one embodiment, aspects of the invention may include twocycloconverter stages with the HF transformer sandwiched in between.However, to support cycloconversion, four-quadrant high-frequencysemiconductor devices may be needed, which are not available in existingconfiguration of the prior art. Therefore, embodiments of the inventionmay include a plurality of available of high-frequency devices toachieve the same realization.

In yet another approach, and as illustrated in FIG. 13 b , anotherdiagram may illustrate a SST system to mitigate the need forfour-quadrant devices according to some embodiments. In one example, afront-end of the HF transformer 1120 (e.g., the LFAC/HFAC) may be partof a two-stage power-electronic system 1110 comprising an ac/dcrectifier 1112 followed by a dc/ac HF inverter 1114; while an output endof the HF transformer 1122 (e.g., the HFAC/LFAC) comprises a rectifier1116 followed by a dc/ac HF inverter 1118. Such an aspect of theinvention, therefore, may provide four stages of power conversion whileeliminating the need for four-quadrant devices.

In contrast, aspects of the invention, such as one embodiment as shownin FIG. 4 a , provide a single stage approach with a modular, flexible,and scalable power-conversion system that provides ease of manufacture.Such an approach may reduce the number of devices, semiconductor devicecost, and the complexity of the system for a comparable conventionalSST. Compared to 60/50-Hz flux cycle LPT, embodiments of the inventionmay reduce the size and weight of the transformer significantly.Embodiments of the invention may also reduce the need forelectromagnetic-interference (EMI) filtering since it yields input andoutput current continuity. In one example, FIG. 4 a ’s La1 and La2 inblock 402 preceded and followed by Ca1 and Ca4 yield reduced source andload current ripples due to input-output continuity. This configurationmay mitigate the need for an electromagnet interference (EMI) filter. Incontrast and as an example, a buck converter in contrast will have apulsating input current which will require a larger EMI filter.

In another embodiment, as shown in FIG. 4 b where the input and outputcurrent ripple may be reduced even further due to integration of theinductors and the single-phase system yields reduced current ripples.This has a profound effect on reducing the need for an EMI filter.

Additionally, aspects of the invention, based on its inductive andcapacitive variant, may provide a dual capability of stepping up andstepping down of the voltage. In this example, this approach creates asymmetry of the topology while providing the ability to reduce the sizeof the high-frequency-based ac/ac system via magnetic integration.

It may be understood that the present invention as described above maybe implemented in the form of control logic using computer software in amodular or integrated manner. Based on the disclosure and teachingsprovided herein, a person of ordinary skill in the art may know andappreciate other ways and/or methods to implement the present inventionusing hardware, software, or a combination of hardware and software.

The above description is illustrative and is not restrictive. Manyvariations of embodiments may become apparent to those skilled in theart upon review of the disclosure. The scope embodiments should,therefore, be determined not with reference to the above description,but instead should be determined with reference to the pending claimsalong with their full scope or equivalents.

One or more features from any embodiment may be combined with one ormore features of any other embodiment without departing from the scopeembodiments. A recitation of “a”, “an” or “the” is intended to mean “oneor more” unless specifically indicated to the contrary. Recitation of“and/or” is intended to represent the most inclusive sense of the termunless specifically indicated to the contrary.

One or more of the elements of the present system may be claimed asmeans for accomplishing a particular function. Where suchmeans-plus-function elements are used to describe certain elements of aclaimed system it may be understood by those of ordinary skill in theart having the present specification, figures and claims before them,that the corresponding structure includes a computer, processor, ormicroprocessor (as the case may be) programmed to perform theparticularly recited function using functionality found in a computerafter special programming and/or by implementing one or more algorithmsto achieve the recited functionality as recited in the claims or stepsdescribed above. As would be understood by those of ordinary skill inthe art that algorithm may be expressed within this disclosure as amathematical formula, a flow chart, a narrative, and/or in any othermanner that provides sufficient structure for those of ordinary skill inthe art to implement the recited process and its equivalents.

While the present disclosure may be embodied in many different forms,the drawings and discussion are presented with the understanding thatthe present disclosure is an exemplification of the principles of one ormore inventions and is not intended to limit any one embodiments to theembodiments illustrated.

Further advantages and modifications of the above-described system andmethod may readily occur to those skilled in the art.

The disclosure, in its broader aspects, is therefore not limited to thespecific details, representative system and methods, and illustrativeexamples shown and described above. Various modifications and variationsmay be made to the above specification without departing from the scopeor spirit of the present disclosure, and it is intended that the presentdisclosure covers all such modifications and variations provided theycome within the scope of the following claims and their equivalents.

What is claimed is:
 1. A solid-state power-conversion system comprising:a single-stage first block comprising at a first input side: at leastone first input switch; at least one first input inductor, and at leastone first input capacitor; and at a first output side: at least onefirst output switch; at least one first output inductor, and at leastone first output capacitor; and a first high-frequency transformer(HFT); a single-stage second block comprising at a second input side: atleast one second input switch; at least one second input inductor, andat least one second input capacitor; and at a second output side: atleast one second output switch; at least one second output inductor, andat least one second output capacitor; and a second HFT; and wherein thesecond block and first block are connected in series at input and outputsides.
 2. The solid-state power-conversion system of claim 1, whereinthe first input inductor, the first output inductor, and the first HFTform a common magnetic core.
 3. The solid-state power-conversion systemof claim 1, wherein fluxes of the at least one first input inductor andthe at least one first output inductor are built up in response to theat least one first input switch being energized, or wherein fluxes ofthe at least one second input inductor and the at least one secondoutput inductor are built up in response to the at least one secondinput switch being energized.
 4. The solid-state power-conversion systemof claim 1, wherein energies of the at least one first input inductorand the at least one first output inductor are transferred to the atleast one first input capacitor and the at least one first outputcapacitor in response to the at least one first output switch beingenergized or wherein energies of the at least one second input inductorand the at least one second output inductor are transferred to the atleast one second input capacitor and the at least one second outputcapacitor in response to the at least one second output switch beingenergized.
 5. The solid-state power-conversion system of claim 1,further comprising at least one loss-mitigating soft switching circuit,wherein the at least one soft switching circuit comprises at least aswitch, a capacitor, and an inductor.
 6. The solid-statepower-conversion system of claim 1, further comprising a switch controlfor the first block or the second block to provide switching states andswitching sequences for switches of each of the first block and thesecond block, wherein the switch control for the first block or thesecond block is configured to coordinate the switching states and thesequences of the switch states for each of the first block and thesecond block.
 7. The solid-state power-conversion system of claim 6,wherein the switch control for the first block and the switch controlfor the second block are configured to coordinate with each other. 8.The solid-state power-conversion system of claim 1, further comprising athird block comprising at a third input side: at least one third inputswitch; at least one third input inductor, and at least one third inputcapacitor; and at a third output side: at least one third output switch;at least one third output inductor, and at least one third outputcapacitor; a third HFT; wherein the first block, the second block, andthe third block are connected in series at input and output sides.
 9. Asolid-state power-conversion system having at least two alternatingcurrent (ac) to ac (ac/ac) modules comprising: at least two single-phaseblocks in each of the at least two ac/ac modules, each of the twosingle-phase blocks comprises at a first input side: at least one firstinput switch; and at least one first input capacitor; and at a firstoutput side: at least one first output switch; and at least one firstoutput capacitor; and a high frequency transformer (HFT); wherein eachof the two single-phase modules is connected in series at the input andthe output to each other.
 10. The solid-state power-conversion system ofclaim 9, further comprising at least an input inductor outside at leastone of the at least two ac/ac modules.
 11. The solid-statepower-conversion system of claim 9, further comprising at least anoutput inductor outside at least one of the at least two ac/ac modules.12. The solid-state power-conversion system of claim 9, furthercomprising a switch control for each of the two single-phase blocks toprovide switching states and switching sequences of the switching statesfor each of the blocks, wherein the switch control is configured tocoordinate the switching states and the sequences of the switchingstates for each of the blocks.
 13. The solid-state power-conversionsystem of claim 12, wherein the switch control for each of the twosingle-phase blocks in the two ac/ac modules are configured tocoordinate with the switch control in the modules.
 14. The solid-statepower-conversion system of claim 9, further comprising at least oneloss-mitigating soft switching circuit, wherein the soft switchingcircuit comprises at least a switch, a capacitor, and an inductor. 15.The solid-state power-conversion system of claim 9, wherein fluxes ofthe at least one first input inductor and the at least one first outputinductor are built up in response to the at least one first input switchbeing energized.
 16. The solid-state power-conversion system of claim 9,wherein energies of the at least one first input inductor and the atleast one first output inductor are transferred to the at least onefirst input capacitor and the at least one first output capacitor inresponse to the at least one first output switch being energized.
 17. Athree-phase solid-state power-conversion system comprising: at leastthree blocks in at least one alternating current (ac) to ac (ac/ac)module, each of the three blocks comprises at an input side: at leastone input switch; at least one input inductor, and at least one inputcapacitor; and at an output side: at least one output switch; at leastone output inductor, and at least one output capacitor; and ahigh-frequency transformer (HFT); and wherein the each of the threeblocks is connected in series at the input and the output to each other.18. The solid-state power-conversion system of claim 17, furthercomprising a switch control for each of the three single-phase blocks toprovide switching states and switching sequences for a switch of each ofthe blocks, wherein the switch control is configured to coordinate theswitching states and the sequences of the switching states for each ofthe blocks.
 19. The solid-state power-conversion system of claim 17,wherein the switch control for each of the three single-phase blocks inthe at least one ac/ac module is configured to coordinate with theswitch control in the at least one module.
 20. The solid-statepower-conversion system of claim 17, further comprising at least oneloss-mitigating soft switching circuit, wherein the soft switchingcircuit comprises at least a switch, a capacitor, and an inductor.